What formula does this use for elapsed time?

The Hale formula: ET = 5.825 × (Weight / HP)^(1/3). It was developed empirically from drag strip data and gives a reasonable estimate for street-prepped and bracket race cars on a well-prepared track surface.

What formula does this use for trap speed?

The trap speed formula: MPH = 234 × (HP / Weight)^(1/3). This is derived from the kinetic energy at the finish line and is consistent with the Hale ET formula — both assume the same efficiency constant.

Should I enter flywheel HP or wheel HP?

Use wheel HP (WHP) for the most accurate predictions, since it accounts for drivetrain losses. If you only have flywheel HP, typical drivetrain loss is 15–20%, so multiply flywheel HP by 0.80–0.85 to estimate WHP.

How accurate are the results?

For a street-prepped car on a prepped track with good traction, these formulas are typically within 3–8% of actual times. Poor traction, excessive aerodynamic drag, and non-standard transmissions can cause larger deviations.

What weight should I enter?

Use the actual race weight — curb weight plus driver (around 180 lb) minus any ballast removed for the run. A more precise weight input produces a more accurate prediction.

Can this predict 1/8-mile times?

Not directly — this tool calculates quarter-mile (1/4 mile) stats only. A rough rule of thumb is that the eighth-mile ET is roughly 64% of the quarter-mile ET, but that approximation carries additional uncertainty.

Quarter Mile Calculator

Name: Quarter Mile Calculator
Availability: InStock
Author: Nham Vu

Enter vehicle weight and horsepower to instantly estimate your quarter-mile elapsed time and trap speed.

Vehicle Specifications

Uses the Hale formula: ET = 5.825 × (Weight / HP)^1/3 & MPH = 234 × (HP / Weight)^1/3

Vehicle Weight (lb)

Include driver and fuel weight

Horsepower (HP)

Wheel HP gives the most accurate result

Typical Reference Points

Average Stock Car

3,500 lb / 250 HP

≈ 14.2 s / 97 mph

Sport Coupe

3,000 lb / 400 HP

≈ 11.8 s / 116 mph

Built Race Car

2,400 lb / 700 HP

≈ 9.8 s / 141 mph

Results assume good traction on a prepped surface. Actual times vary with driver skill, tires, and conditions.

Summary

Enter vehicle weight and horsepower to instantly estimate your quarter-mile elapsed time and trap speed.

How it works

Enter the vehicle's total weight in pounds, including driver and fuel.
Enter the vehicle's wheel horsepower or flywheel horsepower.
Estimated ET and trap speed appear instantly.
Adjust either input to explore different weight or power combinations.
Use the Reset button to clear all fields.

Use cases

Estimate your car's quarter-mile performance before a track day.
See how a weight reduction or power upgrade changes your predicted ET.
Cross-check published 0–60 and quarter-mile claims against the formulas.
Plan bracket racing dial-ins based on predicted elapsed time.
Compare stock vs. modified configurations side by side.
Verify trap speed readings from a timing slip against expected power.
Set realistic performance goals for a build project.

Frequently Asked Questions

Related tools

Horsepower Calculator Engine Displacement Calculator Torque To Hp Calculator

Last updated: 2026-05-29 · Reviewed by Nham Vu